Don't get me wrong, I think Fooger may be right that Marienburg can definitely recoup its losses in the coming years, but my point is that the other Houses may think differently and someone might do something in panic to try to stop a project half a continent away.
Ships have a much greater carrying capacity than any land transportation in this setting, don't get tired and can keep traveling 24 hours a day, so they can cover a much greater distance provided that the places they wish to travel to are near water. It's absolutely worthwhile.